Re: 02 Mustang Vert - Wet carpet back passenger side!
From another forum on the same problem ,
" Ok after having the leak problem myself and tearing out the innards of the car (2003 Vert) here is what I learned.
1. There are two drains in the front cowl on either side of the car. Where the A pillar meets the body and fender.
Put a garden hose up there and look for water coming out under the car.
2. In the back just in front of the rear wheels on each side there are drain holes. They are easier to see if you remove the plastic ground effects panels.
Believe it or not, it is NORMAL for water to run through the car. What happens is it will enter the front and run through the frame under the plastic rocker panel covers, or whatever they are called, the things that say Mustang on them. If you pop them off, park on an angle with the front up, and flush the front of the car, you can look through holes in the frame and see the water running through there.
The water SHOULD exit at little slits in the rear which are behind the rear side mounted speakers. Water going in from around the metal trim at the edge of the vert top will also collect in here and somehow make it's way to these slits. With the top down if you look in on the side toward the front where the springs and top hydraulic lift tubes are located you might be able to see the slits.
If not, remove the rear seat or the speaker and peek in there and you will see them.
The problem is they clog and then water collects under the rear seat, rear floor pans.
In my case the seam where the passenger side floor pan is welded to the frame (where the water runs through) didn't have enough seam sealer on it so when the water ran through the frame, it never made it to the rear drains and instead ran out into the rear passenger side floor pan making a mess.
Chances are your drains in the rear/front are just clogged. "